1. Field of the Invention
The present invention relates to a developing apparatus using monocomponent magnetic developer for developing electrostatic latent images.
2. Description of the Related Art
There exist developing apparatuses using monocomponent developer, each comprising an electrostatic latent image carrying body with a developer carrying body positioned opposite thereto. In operation, the developer carrying body is covered with a thin layer of the developer so that the developer is transferred from the developer carrying body to the electrostatic latent image carrying body for visual image development. The developing process takes place in what is known as the developing region of the apparatus where the two bodies are positioned opposite to each other.
In this type of developing apparatus, the developer stocked within a developer housing is first applied onto the surface (i.e., sleeve) of the developer carrying body. As the sleeve rotates in the direction of its circumference, the developer is transported over the entire sleeve surface. The developer carrying body is exposed where the developer housing is opened toward the electrostatic latent image carrying body. It is in that position of exposure that the developer carrying body is furnished opposite and close to the electrostatic latent image carrying body.
A developer trimming member is provided to form a thin layer of developer over the developer carrying body. This member is made illustratively of a stainless steel spring material (e.g., SUS 304 CSP 3/4H) tipped with a silicone rubber part. Also furnished are side sealing members that prevent developer leakage from portions other than the image region in the axial direction of the developer carrying body as well as from the gap between the developer carrying body and the developer housing.
The arrangements above constitute the basic specifications according to which a large number of developing apparatuses have been developed and commercially employed in printers and copiers of low process speeds.
Today, developing apparatuses are required to provide ever higher process speeds (20 CPM or more in A4 size), longer life (the same as that of the connected image forming apparatus), and higher reliability (elimination of secondary trouble in image quality caused by disturbed toner supply or transport). Of these requirements, that of the prolonged life has been met by recently introduced developing apparatuses using monocomponent developer in a specific manner. That is, these apparatuses are capable of eliminating the need for the periodical change of developer (carrier), the need having long being associated with developing apparatuses using two-component developer.
There were many cases in which the above-mentioned requirements were not meet by hard copy developing apparatus because of their irregularities. More specifically, the difficulty was attributed to three major factors: (1) a failed side sealing member (resulting in toner leaks), (2) the developer trimming member deformed (by interference with the developer carrying body, temperature change, entry of impurities, etc.), and (3) a worn-out silicone rubber part at the tip of the developer trimming member.
The factor (1) above (side sealing member failure) has been resolved by improvements disclosed in U.S. patent application Ser. No. 08/048,231 filed by the same applicant having filed this invention. Specifically, two improvements are involved: (A) the side sealing members are kept either in non-contact relation to the developer trimming member or are brought into contact with it under a force level such as not to deform it; and (B) the developer trimming member is held in contact with the developer carrying body at the three o'clock position of the latter (perpendicular to the sleeve surface) to optimize the trimming pole position, coupled with partitions for removing deposits of excess toner.
The factor (2) above (deformed developer trimming member) has been resolved by another improvement proposed by the applied patent cited, Specifically, the improvement involves having the developer trimming member bonded to a developer housing fastening plate made of the same material, i.e., the SUS 304 CPS 3/4H spring material furnished with a silicone rubber part.
However, the factor (3) above (worn-out silicone rubber part) has yet to be resolved by any of the improvements proposed by the applied patent above. In may cases of printers and copiers of the past with relatively short service lives (equivalent to 100,000 copies or less), the life of the developer trimming member used to be the same as, or shorter than, that of the connected image forming apparatus. Where necessary, the failed developer trimming member or the entire developing apparatus was replaced to deal with the problem of silicone rubber wear.
With the above factors (1) and (2) resolved and with the developing apparatuses improved correspondingly in performance, higher process speeds (20 CPM or more in A4 size) are being required of and implemented by these apparatuses. Whereas the improvements of the applied patent cited above have been implemented and the high process speed requirement is being met, there still remains the problem of the costly service addressing the trimming member replacement.